This paper presents how an information processing model can be used to design human-computer integrated assembly planning systems. The information processing model provides a common, systematic basis to define human and computer activities in assembly planning. Relevant research issues are discussed, concerning a unified process of assembly planning, the compatibility between decisions, rules and information involved in assembly planning, and the effectiveness of an integrated, graphic representation for exchange of information and problem space between different stages of assembly planning and across the human-computer interface.